1. Field of the Invention
The present invention relates to an oscillator sieving a toner used in image forming apparatus and other raw materials.
2. Description of the Related Art
Methods of visualizing electrostatic latent image information such as an electrophotographic method are used in various fields. The electrophotographic method includes charging, irradiating to form an electrostatic latent image on a photoreceptor, developing the electrostatic latent image with a developer including a toner to form a toner image, and transferring and fixing the toner image. The developer includes a two-component developer formed of a toner and a carrier and a one-component developer formed of only a magnetic or non-magnetic toner. In either case, a toner is a main component. Methods of preparing a toner include dry methods such as pulverization methods; and wet methods such as emulsion polymerization agglutination methods, suspension polymerization methods, drying in liquid methods and rotational phase emulsification methods.
The dry method using the pulverization method uniformly mixing and dispersing materials such as a binder resin, a release agent, a colorant and an optional charge controlling agent with a press kneader, an extruder or a media disperser. Then, the mixed materials are collided to a target mechanically or under a jet stream such that the resultant toner has a desired particle diameter, and further classified such that the resultant toner has a sharp particle diameter distribution. The toner having a desired particle diameter is formed of a binder resin and a colorant, and further includes an inorganic particulate material as an external additive in many cases to improve its fluidity. The toner has sufficient fluidity with the externally added inorganic particulate material, and produces high-quality images without blank images. However, when the toner and the external additive are stirred and mixed, the toners agglutinate with each other or with the external additive, or the external additives agglutinate with each other due to generation of eat and collision of the materials in high-speed mixing.
Meanwhile, the wet methods have problems of aggregates of materials made in the process of emulsification, suspension and drying; and plate-shaped coarse particles caused by materials adhering to the emulsification, suspension and reaction containers, and the stirring blades.
The aggregates in the dry methods and the coarse particles in the wet methods cause a non-uniform gap between a photoreceptor and a transfer material, i.e., a transfer gap in a transfer process in image forming apparatus. The non-uniform gap causes uneven image density and toner scattering on non-image areas. A toner including the aggregates and coarse particles is likely to produce images having uneven image density caused by charge difference due to particle size difference. The aggregates and coarse particles are large elements deteriorating image quality, such as uneven image density and toner scattering on non-image areas. Further, they cause toner scattering in developing of image forming apparatus, resulting in contamination therein.
The aggregates and coarse particles made in the process of preparing a toner cause deterioration of image quality and contamination in image forming apparatus. In order to remove the aggregates and the coarse particles from a toner, conventional toner preparation processes include a sieving process sieving a toner with a sieve.
A toner including the aggregates and coarse particles is fed on a screen of the sieve having a predetermined opening diameter, and mechanical oscillation such as three-dimensional motion is applied to the screen for sieving. The oscillation sieve can separate the toner having passed the screen and the aggregates and coarse particles not having passed the screen. Japanese Patent No. JP-2840714-B1 (Japanese published unexamined application No. JP-H07-275081-A) discloses an oscillation sieve including a guide member at a coarse powder exhaust, guiding the aggregates and coarse particles thereto to be discharged. Japanese published unexamined application No. JP-H11-033488-A discloses an oscillation sieve including an exhaust inhibitor on the screen, preventing the aggregates and coarse particles remaining thereon from discharging from a coarse powder exhaust when sieving. The oscillation sieve prevents the aggregates and coarse particles from discharging from the coarse powder exhaust when sieving, and discharge them therefrom only when doing discharge operation. Japanese published unexamined application No. JP-2006-507934-A discloses an oscillation sieve including a spiral guide member guiding the aggregates and coarse particles fed to the center of a circular screen to a coarse powder exhaust on an outer circumference of the screen.
The oscillation sieves disclosed in Japanese Patent No. JP-2840714-B1 (Japanese published unexamined application No. JP-H07-275081-A), and Japanese published unexamined applications Nos. JP-H11-033488-A and JP-2006-507934-A remove the aggregates and coarse particles formed before sieving process. However, the oscillation sieve disclosed in Japanese Patent No. JP-2840714-B1 (Japanese published unexamined application No. JP-H07-275081-A) discharges even materials having a desired particle diameter, passable through the screen, resulting in lowering of yield rate.
The oscillation sieve disclosed in Japanese published unexamined application No. JP-H11-033488-A prevents materials having a desired particle diameter from flowing out to the coarse powder exhaust. When the oscillation sieve discharges nothing therefrom when sieving, the aggregates and coarse particles unpassable through the screen keep on remaining thereon. When the aggregates and coarse particles keep on remaining on the screen, their ratios on the screen are high and the screen is likely to be clogged, resulting in deterioration of sieving capability. In order to avoid this, sieving operation is switched to discharge operation at a predetermined time to discharge the aggregates and coarse particles on the screen from the coarse powder exhaust. However, sieving operation needs stopping to do discharge operation, and productivity largely deteriorates in long-time continuous operation.
In the oscillation sieve disclosed in Japanese published unexamined application No. JP-2006-507934-A, materials fed at the center of the circular screen are spirally transferred along the spiral guide member on the screen to the coarse powder exhaust formed at the outer circumference of the screen. When materials are spirally transferred, time since they are fed on the screen until discharged at the coarse powder exhaust is assured, and the aggregates and coarse particles are continuously discharged. When time since materials on the screen until discharged at the coarse powder exhaust is assured, those having a desired particle diameter passable through the screen have more opportunity to be sieved, which prevents the yield rate from lowering in the oscillation sieve disclosed in Japanese Patent No. JP-2840714-B1 (Japanese published unexamined application No. JP-H07-275081-A). In addition, materials including the aggregates and coarse particles in a large ratio are continuously discharged from the coarse powder exhaust, which prevents the ratio of the aggregates and coarse particles from increasing, the screen from being clogged, and sieving capability from deteriorating even in long-time operations. Further, sieving operation does not need stopping to do discharge operation as the oscillation sieve disclosed in Japanese published unexamined application No. JP-H11-033488-A, and large deterioration of productivity in long-time continuous operation can be prevented.
However, the oscillation sieve disclosed in Japanese published unexamined application No. JP-2006-507934-A uses a metallic member as a guide member. A high-harness guide member formed of a metal cannot follow the oscillation of the screen. The guide member is fixed on the screen with an adhesive in the oscillation sieve disclosed in Japanese published unexamined application No. JP-2006-507934-A. When a part of the guide member is fixed on the screen, a gap between the guide member which cannot follow the oscillation of the screen and the screen opens and closes at an unfixed part. Meanwhile, when the whole area of the guide member contacting the screen is fixed thereon with an adhesive, the guide member which cannot follow the oscillation of the screen is peeled from the screen, resulting in an unfixed part opening and closing a gap between the guide member and the screen. When materials enter the gap, they are repeatedly crushed therebetween to be solidified, resulting in new aggregates occasionally. In addition, when the gap between the guide member and the screen opens and closes, they are heated by friction therebetween and materials on the screen melt and agglutinate, resulting in new aggregates occasionally. The new aggregates are removed with the aggregate included in materials before sieved, resulting in lowering of yield rate.
Because of these reasons, a need exist for an oscillation sieve using a screen, which prevents its yield rate and sieving capability from lowering, and a new aggregate from generating.